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Carol L Colby - One of the best experts on this subject based on the ideXlab platform.
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representation of the ipsilateral visual field by neurons in the macaque lateral intraparietal cortex depends on the foreBrain commissures
Journal of Neurophysiology, 2010Co-Authors: Catherine A Dunn, Carol L ColbyAbstract:Our eyes are constantly moving, allowing us to attend to different visual objects in the environment. With each eye movement, a given object activates an entirely new set of visual neurons, yet we perceive a stable scene. One neural mechanism that may contribute to visual stability is remapping. Neurons in several Brain regions respond to visual stimuli presented outside the receptive field when an eye movement brings the stimulated location into the receptive field. The stored representation of a visual stimulus is remapped, or updated, in conjunction with the saccade. Remapping depends on neurons being able to receive visual information from outside the classic receptive field. In previous studies, we asked whether remapping across hemifields depends on the foreBrain commissures. We found that, when the foreBrain commissures are transected, behavior dependent on accurate spatial updating is initially impaired but recovers over time. Moreover, neurons in lateral intraparietal cortex (LIP) continue to remap information across hemifields in the absence of the foreBrain commissures. One possible explanation for the preserved across-hemifield remapping in Split-Brain animals is that neurons in a single hemisphere could represent visual information from both visual fields. In the present study, we measured receptive fields of LIP neurons in Split-Brain monkeys and compared them with receptive fields in intact monkeys. We found a small number of neurons with bilateral receptive fields in the intact monkeys. In contrast, we found no such neurons in the Split-Brain animals. We conclude that bilateral representations in area LIP following foreBrain commissures transection cannot account for remapping across hemifields.
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dynamic circuitry for updating spatial representations i behavioral evidence for interhemispheric transfer in the Split Brain macaque
Journal of Neurophysiology, 2005Co-Authors: Rebecca A Berman, Carol L Colby, Laura M Heiser, Richard C SaundersAbstract:Internal representations of the sensory world must be constantly adjusted to take movements into account. In the visual system, spatial updating provides a mechanism for maintaining a coherent map of salient locations as the eyes move. Little is known, however, about the pathways that produce updated spatial representations. In the present study, we asked whether direct cortico-cortical links are required for spatial updating. We addressed this question by investigating whether the foreBrain commissures-the direct path between the two cortical hemispheres-are necessary for updating visual representations from one hemifield to the other. We assessed spatial updating in two Split-Brain monkeys using the double-step task, which involves saccades to two sequentially appearing targets. Accurate performance requires that the representation of the second target be updated to take the first saccade into account. We made two central discoveries regarding the pathways that underlie spatial updating. First, we found that Split-Brain monkeys exhibited a selective initial impairment on double-step sequences that required updating across visual hemifields. Second, and most surprisingly, these impairments were neither universal nor permanent: the monkeys were ultimately able to perform the across-hemifield sequences and, in some cases, this ability emerged rapidly. These findings indicate that direct cortical links provide the main substrate for updating visual representations, but they are not the sole substrate. Rather, a unified and stable representation of visual space is supported by a redundant cortico-subcortical network with a striking capacity for reorganization.
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dynamic circuitry for updating spatial representations ii physiological evidence for interhemispheric transfer in area lip of the Split Brain macaque
Journal of Neurophysiology, 2005Co-Authors: Laura M Heiser, Carol L Colby, Rebecca A Berman, Richard C SaundersAbstract:With each eye movement, a new image impinges on the retina, yet we do not notice any shift in visual perception. This perceptual stability indicates that the Brain must be able to update visual representations to take our eye movements into account. Neurons in the lateral intraparietal area (LIP) update visual representations when the eyes move. The circuitry that supports these updated representations remains unknown, however. In this experiment, we asked whether the foreBrain commissures are necessary for updating in area LIP when stimulus representations must be updated from one visual hemifield to the other. We addressed this question by recording from LIP neurons in Split-Brain monkeys during two conditions: stimulus traces were updated either across or within hemifields. Our expectation was that across-hemifield updating activity in LIP would be reduced or abolished after transection of the foreBrain commissures. Our principal finding is that LIP neurons can update stimulus traces from one hemifield to the other even in the absence of the foreBrain commissures. This finding provides the first evidence that representations in parietal cortex can be updated without the use of direct cortico-cortical links. The second main finding is that updating activity in LIP is modified in the Split-Brain monkey: across-hemifield signals are reduced in magnitude and delayed in onset compared with within-hemifield signals, which indicates that the pathways for across-hemifield updating are less effective in the absence of the foreBrain commissures. Together these findings reveal a dynamic circuit that contributes to updating spatial representations.
Stanislas Dehaene - One of the best experts on this subject based on the ideXlab platform.
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Splitting of the p3 component during dual task processing in a patient with posterior callosal section
Cortex, 2013Co-Authors: Guido Hesselmann, Lionel Naccache, Stanislas Dehaene, Laurent D CohenAbstract:When two concurrent sensorimotor tasks have to be performed at a short time interval, the second response is generally delayed at a central decision stage. However, in patients who have undergone full or partial transection of foreBrain fibers connecting the two hemispheres (Split-Brain), independent structures subserving all processing stages should reside in each disconnected hemisphere, thus predicting parallel processing of dual tasks. Surprisingly, this prediction is usually not verified behaviorally. We reasoned that Brain imaging with high-density recordings of event-related potentials (ERPs) could clarify the extent and limits of parallel processing in callosal patients. We studied a patient (AC) with posterior callosal section in a lateralized number-comparison task. Behaviorally, the Split-Brain patient showed robust dual-task interference, superficially similar to the psychological refractory period (PRP) effect in the control group of 14 healthy subjects, but significantly different in important aspects such as slowing of response times in the first task. Analysis of ERPs revealed that the parietal P3 component became Split into distinct contralateral components in the patient, and was dramatically reduced for targets in his left visual field. In contrast to the control group, P3 latencies showed minimal to nonexistent postponement related to dual-task processing in the patient. In summary, our findings suggest that the left and right hemisphere networks normally involved in a single distributed "global neuronal workspace" that underlies the generation of the P3 component and serial processing, became strongly decoupled after a posterior callosal lesion.
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The visual word form area. Spatial and temporal characterization of an initial stage of reading in normal subjects and posterior Split-Brain patients
Brain, 2000Co-Authors: Laurent Cohen, Ghislaine Dehaene-lambertz, Marie Anne Hénaff, Stephane Lehericy, Lionel Naccache, Stanislas Dehaene, François MichelAbstract:A standard model of word reading postulates that visual information is initially processed by occipitotemporal areas contralateral to the stimulated hemifield, from whence it is subsequently transferred to the visual word form (VWF) system, a left inferior temporal region specifically devoted to the processing of letter strings. For stimuli displayed in the left visual field, this transfer proceeds from the right to the left hemisphere through the posterior portion of the corpus callosum. In order to characterize the spatial and temporal organization of these processes, reading tasks with Split-field presentation were performed by five control subjects and by two patients suffering from left hemialexia following posterior callosal lesions. The subjects' responses were studied using behavioural measures and functional Brain imaging techniques, providing both high spatial resolution (functional MRI, fMRI) and high temporal resolution (high-density event-related potentials, ERPs). Early visual processing was revealed as activations contralateral to stimulation, located by fMRI in the inferior occipitotemporal region and presumably coincident with area V4. A negative wave occurring 150-160 ms post-stimulus, also strictly contralateral to stimulation, was recorded over posterior electrodes. In contrast with these hemifield-dependent effects, the VWF system was revealed as a strictly left-hemispheric activation which, in control subjects, was identical for stimuli presented in the left or in the right hemifield and was located in the middle portion of the left fusiform gyrus. The electrical signature of the VWF system consisted of a unilateral sharp negativity, recorded 180-200 ms post-stimulus over left inferior temporal electrodes. In callosal patients, due to the inability of visual information to pass across the posterior part of the corpus callosum, the VWF system was activated only by stimuli presented in the right visual field. Similarly, a significant influence of the word/non-word status on ERPs recorded over the left hemisphere was discernible for either hemifield in controls, while it affected only right-hemifield stimuli in callosal patients. These findings provide direct support for the main components of the classical model of reading and help specify their timing and cerebral substrates.
Michael S. Gazzaniga - One of the best experts on this subject based on the ideXlab platform.
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right hemisphere dominance for understanding the intentions of others evidence from a Split Brain patient
Case Reports, 2009Co-Authors: Stephanie Ortigue, Danielle R. King, Michael B Miller, Michael S. Gazzaniga, Scott T GraftonAbstract:Understanding the actions performed by other people is a key aspect of social interaction, including in clinical settings where patients are learning from therapists and caregivers. While lesions of the left cerebral hemisphere induce praxic disorders, the hemispheric specialisation of intention understanding remains unclear. Do patients with a right hemispheric lesion understand the intentions of other people properly? The present study investigates how a Split-Brain patient understands the means (what) and intentions (why) of the actions of other people. Results show a significant left hemispheric dominance for understanding what is done, and a significant right hemispheric dominance for understanding why an action is carried out. This discovery might have important clinical implications in neurological patients, especially when those with right hemisphere lesions are faced with important decisions related to the interpretation of other’s intentions.
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the ventriloquist in motion illusory capture of dynamic information across sensory modalities
Cognitive Brain Research, 2002Co-Authors: Salvador Sotofaraco, Michael S. Gazzaniga, Jessica Lyons, Alan KingstoneAbstract:Integrating dynamic information across the senses is crucial to survival. However, most laboratory studies have only examined sensory integration for static events. Here we demonstrate that strong crossmodal integration can also occur for an emergent attribute of dynamic arrays, specifically the direction of apparent motion. The results of the present study show that the perceived direction of auditory apparent motion is strongly modulated by apparent motion in vision, and that both spatial and temporal factors play a significant role in this crossmodal effect. We also demonstrate that a Split-Brain patient who does not perceive visual apparent motion across the midline is immune to this audiovisual dynamic capture effect, highlighting the importance of motion being experienced in order for this new multisensory illusion to occur.
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cerebral specialization and interhemispheric communication does the corpus callosum enable the human condition
Brain, 2000Co-Authors: Michael S. GazzanigaAbstract:Summary The surgical disconnection of the cerebral hemispheres half-Brain. By having the callosum serve as the great communication link between redundant systems, a precreates an extraordinary opportunity to study basic existing system could be jettisoned as new functions neurological mechanisms: the organization of the sensory developed in one hemisphere, while the other hemisphere and motors systems, the cortical representation of the could continue to perform the previous functions for both perceptual and cognitive processes, the lateralization of half-Brains. Split-Brain studies have also revealed the function, and, perhaps most importantly, how the divided complex mosaic of mental processes that participate in Brain yields clues to the nature of conscious experience. human cognition. And yet, even though each cerebral Studies of Split-Brain patients over the last 40 years hemisphere has its own set of capacities, with the left have resulted in numerous insights into the processes of hemisphere specialized for language and speech and perception, attention, memory, language and reasoning major problem-solving capacities and the right abilities. When the constellation of findings is considered hemisphere specialized for tasks such as facial recognition as a whole, one sees the cortical arena as a patchwork of and attentional monitoring, we all have the subjective specialized processes. When this is considered in the light experience of feeling totally integrated. Indeed, even of new studies on the lateralization of functions, it becomes though many of these functions have an automatic quality reasonable to suppose that the corpus callosum has to them and are carried out by the Brain prior to our enabled the development of the many specialized systems conscious awareness of them, our subjective belief and by allowing the reworking of existing cortical areas feeling is that we are in charge of our actions. These while preserving existing functions. Thus, while language phenomena appear to be related to our left hemisphere’s emerged in the left hemisphere at the cost of pre-existing interpreter, a device that allows us to construct theories perceptual systems, the critical features of the bilaterally about the relationship between perceived events, actions and feelings. present perceptual system were spared in the opposite
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reflexive joint attention depends on lateralized cortical connections
Psychological Science, 2000Co-Authors: Alan Kingstone, Chris Kelland Friesen, Michael S. GazzanigaAbstract:Joint attention, the tendency to spontaneously direct attention to where someone else is looking, has been thought to occur because eye direction provides a reliable cue to the presence of important events in the environment. We have discovered, however, that adults will shift their attention to where a schematic face is looking—even when gaze direction does not predict any events in the environment. Research with 2 Split-Brain patients revealed that this reflexive joint attention is lateralized to a single hemisphere. Moreover, although this phenomenon could be inhibited by inversion of a face, eyes alone produced reflexive shifts of attention. Consistent with recent functional neuroimaging studies, these results suggest that lateralized cortical connections between (a) temporal lobe subsystems specialized for processing upright faces and gaze and (b) the parietal area specialized for orienting spatial attention underlie human reflexive shifts of attention in response to gaze direction.
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principles of human Brain organization derived from Split Brain studies
Neuron, 1995Co-Authors: Michael S. GazzanigaAbstract:Studies of damaged human Brains have always intrigued neuroscientists. The rich symptomatology that can result is riveting to all who experience examination of such patients. Yet, one of the concerns of basic scientists is that structure-function correlates are difficult to make in the damaged Brain, since the lesions are naturally occurring and usually quite diffuse. In addition to the problem of quantitating the lesion, there has always been concern whether the information gained about the Brain in the presence of lesions is all that useful in understanding normal Brain mechanisms. Are observed effects due to the damage of specific areas or to distant effects? These and other issues have limited the general acceptance of the findings from clinical studies. One of the immediate appeals of the study of patients with surgical division of the foreBrain is that the separate functions of the two cerebral hemispheres can be studied readily in the absence of focal damage. Also, the callosal surgery, while producing damage to the Brain, was discrete damage to a fiber system and not to nuclear areas. In 1961, R. W. Sperry and his colleagues commenced a series of studies on patients who had undergone surgical section of the cerebral commissures in an effort to control their otherwise intractable epilepsy (Bogen et al., 1965). Studies continue on the original patients as well as others and still shed light on the nature of both cortical and subcortical neural networks. In what follows, I review some aspects of this work to illustrate how this initial work has progressed from the early sixties until the time of Sperry's death in the spring of 1994. Patients who undergo so-called Split-Brain surgery all suffer from intractable epilepsy. Prior to their surgery, extensive attempts are made to control their seizures medically. Failure to do so, along with other clinical criteria, finds them candidates for surgical division of the corpus callosum, and in some cases the anterior commissure as well. Although these patients are not normal, the onset of their epilepsy varies and has different etiologies. It has not been possible to correlate any of these variations in their neurologic history with the pattern of results obtained from the cognitive studies. It is known from other data that, in order for there to be significant changes in the normal patterns of cerebral lateralization, a large lesion must occur to one side of the Brain in early childhood (Rasmussen and Milner, 1977).
Richard C Saunders - One of the best experts on this subject based on the ideXlab platform.
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resection of the medial temporal lobe disconnects the rostral superior temporal gyrus from some of its projection targets in the frontal lobe and thalamus
Cerebral Cortex, 2009Co-Authors: Monica Munoz, Mortimer Mishkin, Richard C SaundersAbstract:Auditory memory in the monkey does not appear to extend beyond the limits of working memory. It is therefore surprising that this ability is impaired by medial temporal lobe (MTL) resections, because such lesions spare working memory in other sensory modalities. To determine whether MTL ablations might have caused the auditory deficit through inadvertent transection of superior temporal gyrus (STG) projections to its downstream targets, and, if so, which targets might have been compromised, we injected anterograde tracer (biotinylated dextran amine) in the STG of both the normal and MTL-lesioned hemispheres of Split-Brain monkeys. Interhemispheric comparison of label failed to show any effect of the MTL ablation on efferents from caudal STG, which projects to the inferior prefrontal convexity. However, the ablation did consistently interrupt the normally dense projections from rostral STG to both the ventral medial prefrontal cortex and medial thalamic nuclei. The findings support the possibility that the auditory working memory deficit after MTL ablation is due to transection of downstream auditory projections, and indicate that the candidate structures for mediating auditory working memory are the ventral medial prefrontal cortical areas, the medial thalamus, or both.
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dynamic circuitry for updating spatial representations i behavioral evidence for interhemispheric transfer in the Split Brain macaque
Journal of Neurophysiology, 2005Co-Authors: Rebecca A Berman, Carol L Colby, Laura M Heiser, Richard C SaundersAbstract:Internal representations of the sensory world must be constantly adjusted to take movements into account. In the visual system, spatial updating provides a mechanism for maintaining a coherent map of salient locations as the eyes move. Little is known, however, about the pathways that produce updated spatial representations. In the present study, we asked whether direct cortico-cortical links are required for spatial updating. We addressed this question by investigating whether the foreBrain commissures-the direct path between the two cortical hemispheres-are necessary for updating visual representations from one hemifield to the other. We assessed spatial updating in two Split-Brain monkeys using the double-step task, which involves saccades to two sequentially appearing targets. Accurate performance requires that the representation of the second target be updated to take the first saccade into account. We made two central discoveries regarding the pathways that underlie spatial updating. First, we found that Split-Brain monkeys exhibited a selective initial impairment on double-step sequences that required updating across visual hemifields. Second, and most surprisingly, these impairments were neither universal nor permanent: the monkeys were ultimately able to perform the across-hemifield sequences and, in some cases, this ability emerged rapidly. These findings indicate that direct cortical links provide the main substrate for updating visual representations, but they are not the sole substrate. Rather, a unified and stable representation of visual space is supported by a redundant cortico-subcortical network with a striking capacity for reorganization.
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dynamic circuitry for updating spatial representations ii physiological evidence for interhemispheric transfer in area lip of the Split Brain macaque
Journal of Neurophysiology, 2005Co-Authors: Laura M Heiser, Carol L Colby, Rebecca A Berman, Richard C SaundersAbstract:With each eye movement, a new image impinges on the retina, yet we do not notice any shift in visual perception. This perceptual stability indicates that the Brain must be able to update visual representations to take our eye movements into account. Neurons in the lateral intraparietal area (LIP) update visual representations when the eyes move. The circuitry that supports these updated representations remains unknown, however. In this experiment, we asked whether the foreBrain commissures are necessary for updating in area LIP when stimulus representations must be updated from one visual hemifield to the other. We addressed this question by recording from LIP neurons in Split-Brain monkeys during two conditions: stimulus traces were updated either across or within hemifields. Our expectation was that across-hemifield updating activity in LIP would be reduced or abolished after transection of the foreBrain commissures. Our principal finding is that LIP neurons can update stimulus traces from one hemifield to the other even in the absence of the foreBrain commissures. This finding provides the first evidence that representations in parietal cortex can be updated without the use of direct cortico-cortical links. The second main finding is that updating activity in LIP is modified in the Split-Brain monkey: across-hemifield signals are reduced in magnitude and delayed in onset compared with within-hemifield signals, which indicates that the pathways for across-hemifield updating are less effective in the absence of the foreBrain commissures. Together these findings reveal a dynamic circuit that contributes to updating spatial representations.
Rebecca A Berman - One of the best experts on this subject based on the ideXlab platform.
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dynamic circuitry for updating spatial representations i behavioral evidence for interhemispheric transfer in the Split Brain macaque
Journal of Neurophysiology, 2005Co-Authors: Rebecca A Berman, Carol L Colby, Laura M Heiser, Richard C SaundersAbstract:Internal representations of the sensory world must be constantly adjusted to take movements into account. In the visual system, spatial updating provides a mechanism for maintaining a coherent map of salient locations as the eyes move. Little is known, however, about the pathways that produce updated spatial representations. In the present study, we asked whether direct cortico-cortical links are required for spatial updating. We addressed this question by investigating whether the foreBrain commissures-the direct path between the two cortical hemispheres-are necessary for updating visual representations from one hemifield to the other. We assessed spatial updating in two Split-Brain monkeys using the double-step task, which involves saccades to two sequentially appearing targets. Accurate performance requires that the representation of the second target be updated to take the first saccade into account. We made two central discoveries regarding the pathways that underlie spatial updating. First, we found that Split-Brain monkeys exhibited a selective initial impairment on double-step sequences that required updating across visual hemifields. Second, and most surprisingly, these impairments were neither universal nor permanent: the monkeys were ultimately able to perform the across-hemifield sequences and, in some cases, this ability emerged rapidly. These findings indicate that direct cortical links provide the main substrate for updating visual representations, but they are not the sole substrate. Rather, a unified and stable representation of visual space is supported by a redundant cortico-subcortical network with a striking capacity for reorganization.
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dynamic circuitry for updating spatial representations ii physiological evidence for interhemispheric transfer in area lip of the Split Brain macaque
Journal of Neurophysiology, 2005Co-Authors: Laura M Heiser, Carol L Colby, Rebecca A Berman, Richard C SaundersAbstract:With each eye movement, a new image impinges on the retina, yet we do not notice any shift in visual perception. This perceptual stability indicates that the Brain must be able to update visual representations to take our eye movements into account. Neurons in the lateral intraparietal area (LIP) update visual representations when the eyes move. The circuitry that supports these updated representations remains unknown, however. In this experiment, we asked whether the foreBrain commissures are necessary for updating in area LIP when stimulus representations must be updated from one visual hemifield to the other. We addressed this question by recording from LIP neurons in Split-Brain monkeys during two conditions: stimulus traces were updated either across or within hemifields. Our expectation was that across-hemifield updating activity in LIP would be reduced or abolished after transection of the foreBrain commissures. Our principal finding is that LIP neurons can update stimulus traces from one hemifield to the other even in the absence of the foreBrain commissures. This finding provides the first evidence that representations in parietal cortex can be updated without the use of direct cortico-cortical links. The second main finding is that updating activity in LIP is modified in the Split-Brain monkey: across-hemifield signals are reduced in magnitude and delayed in onset compared with within-hemifield signals, which indicates that the pathways for across-hemifield updating are less effective in the absence of the foreBrain commissures. Together these findings reveal a dynamic circuit that contributes to updating spatial representations.